• Introduction
• Lens Pictures
• Specifications
• Build Quality
• Handling and Focusing
• Image Quality
  • Resolution and Contrast
  • Vignetting
  • Distortion
  • Aberrations and Flare
  • Bokeh
  • Color
• Uses
• Sample Images
• Value
• Conclusion
• Rating

• Exact Name: smc PENTAX-A ZOOM 1:3.5 35~105mm
• Color: black
• Years of Production: 1984 ~ 1989
• Catalog Number: 27097
• Optics
  • Optical Formula: 15 elements in 13 groups
  • Aperture Range: f/3.5 ~ f/22
  • Number of Aperture Blades: 6
  • Minimum Focusing Distance: 1.5 m
  • Maximum Magnification: 0.25 X
• Mechanics
  • Filter Diameter: 67 mm
  • Maximum Diameter: 70 mm
  • Length: 98 mm
  • Weight: 615 g
• Special Features: rotating front element
• Accessories
  • Cap: plastic clip-on cap, 67 mm
  • Fitting Hood(s): clip-on hood: RH-B70
  • Fitting Case(s): hard case: HD-143

Optical Design

I tested the performance of this lens using the Shingle test. The shingle test is similar to the brick wall test, but using a shingle sample board instead. The advantage of the shingle test is that all those little granules on a shingle make for a great resolution and contrast test from center all the way out to the edge and extreme corners. Since the granules are relatively consistent, yet different, you can see any change in resolution, contrast or color from center all the way out to the corners. Keep in mind that 'Sharpness' is a subjective term actually describing the combination of resolution and contrast. A high resolution image with low contrast would often be described as 'soft' to the viewer, while an image with average resolution but excellent contrast would often be described as 'sharp'. For the purposes of this test I try to separate the two contributing factors, but being human, please take in to account that

Graded on a scale of 1 to 100. 1 being a complete loss of image to 100 being tack sharp. This is a subjective test as I do not own any fancy (and expensive) resolution testing equipment or software to gage the resolution of lenses. Your results and opinions may vary.

At 35mm f3.5 center sharpness is good with room for improvement. Border sharpness is less then satisfactory with corner sharpness being pretty low. At f4 things improve a little but major improvement is not seen until f5.6 at which point the edges and corners become usable. At f8 and f11 tis focal length reaches it's peak performance with the center having excellent sharpness and the corners and boarders having very good to excellent sharpness. Beyond f11, diffractions starts to kick in and sharpness begins to fall off.

At 50mm the center sharpness is almost identical to 35mm across the aperture range with corner and border sharpness starting out much better then 35mm at f3.5. Sharpness improves evenly across the frame as the lens is stopped down further with f8 being the peak. At f11 center sharpness drops slightly and diffraction takes it's toll from there on up.

At 80mm there is a slight drop in border and corner sharpness at f3.5 and f4 compared to 50mm, with improvements over 50mm seen at f5.6 where the center is slightly sharper. Peak center performance is seen from f5.6 to f8 with the corners reaching their peak at f11. Again beyond f11 diffraction sets in a sharpness degrades as the lens is stopped down further.

At 105mm f3.5 sharpness across the frame is identical to 50mm f3.5. Improvement is not seen until f5.6 with center sharpness peaking at f8 and f11 and corner sharpness peaking at f11.

Overall this is a very sharp zoom lens with similar sharpness characteristics to prime lenses of similar focal length. It is not quite a sharp as the equivalent prime lenses as most of them would rate a 10 at f8 but it does come very close.

In the images below, the bottom left hand corner of the shingle sample board has some kind of gunk embedded in it so that corner always appears washed out and less sharp even at peak sharpness. In additional test images I have seen no evidence that there is a problem with the lens in the lower left hand corner, so please disregard this area when reviewing the images.

For a quick but effective vignetting test I used the back side of some white vinyl wall board (the type seen in truck stop bathroom walls) as it is a somewhat smooth, flat white surface. Very minor vignetting was observed at 35mm f3.5 and f4 with the light fall off clearing up entirely by f5.6. Similar results were seen at 50mm with no vignetting visible at 80mm. At 105mm vignetting was observed at f3.5 and 4 with none visible at f5.6 or above. Vignetting at 105mm was more severe then at 35mm, but still minor. This is a film lens being used on an APS-C camera so I honestly did not expect to see much vignetting. On a film body it is probably more pronounced, but on APS-C it is so minor it is barely worth reporting. The pictures below show my observations.

For the distortion sets I used the same vinyl wall board with a grid drawn on it with a magic marker. I assure you, the grid lines are straight, square, and consistently spaced. Years of drafting classes taught me the very valuable skill of drawing a straight line. Unfortunately, though my line drawing skills are still very well developed, my framing skills were lacking slightly in the test. I did not sufficiently align the image with the grid, so you will have to use you imagination a little in interpreting the results. I actually held a clear straight edge up to my LCD monitor to interpret the results.

At 35mm barrel distortion is evident, though not severe and easily corrected in post processing. In practical use the distortion at 35mm will probably not be noticeable. At 50mm distortion is so minor I would say it's just about distortion free. At 80mm the distortion switches to a very slight pincushion shape, but again is so minor it is unlikely to be noticed. At 105mm distortion is a very slight pincushion that is unlikely to be observable in practical use. Overall distortion is very well controlled across the zoom range and will not likely pose an issue in every day use. Keep in mind that these tests were performed on an APS-C camera. On a full frame camera distortion would most likely be more pronounced towards the edges and corners.

Although I will not say that this lens is prone to chromatic aberration (CA), some was observed. Minor CA was observed, specifically purple/blue and green fringing on some high contrast areas. Purple fringing seems to be more of a problem at f3.5 and 4 while green fringing seemed to show itself more at higher apertures. The purple fringing at f3.5 was more pronounced then the green fringing at higher apertures. Green fringing was limited to 1 to 2 pixels width while purple fringing was observed to extend out to 4 pixels in the most extreme example. Again, though it was present, fringing was not pronounced, nor was it ubiquitous. Fringing was not observed to be any more severe at longer focal lengths then short focal lengths. Fringing was only evident in extreme circumstances where other newer lenses would have had much more trouble. This is rather surprising considering this lens lacks low dispersion elements.

Flare was observed though I will not say this lens is prone to it. I will say that it is susceptible to flare. Flare was observed when the lens is pointed in plane or elevated and between 75 and 85 degrees off axis from a bright direct light source such as the sun. Pointed further toward the light source flair disappears until the lens is within 15 to 20 degrees of the light source. All other attempts to produce flair were unsuccessful. When flare is present at 75-85 degrees it appears as a ring or partial ring in the image. Within 20 degrees and/or the light source is in the frame, a veiling flair is observed. Though this lens is not prone to flare, it would definitely benefit from a hood as the front element is large (roughly 67mm) and not recessed into the body more then a few millimeters which makes it susceptible to flare under the right circumstances. Adding a lens hood would probably increase the ability to take pictures with this lens on sunny days. For a lens with fifteen elements and even more glass surfaces, this lens is quite resistant to flair. I guess that is the advantage of SMC coating.

This is the category that I think is the major weakness of this lens. Bokeh is a mixed bag with this unique zoom. It can be harsh and unpleasing or smooth and unobtrusive. In close up macro shots, the bokeh is usually smooth and creamy. In standard focus mode, at any focal length the bokeh can be either harsh or smooth depending on the background lighting. When the background is brighter and more directly lit then the subject the highlights take on a very busy harsh look. At f3.5 in most situations the bokeh is too busy and distracting. Some might even call it ugly. It almost has an impressionistic feel to it that some might find appealing. Personally I'm not crazy about it, but I can see how in certain situations the busy bokeh at f3.5 might add an interesting look to a picture.

I actually found that bokeh improves with higher apertures, though still a little busy it is smoother and less distracting. Bokeh is actually quite nice and smooth with darker or more consistent backgrounds that do not contain too many bright highlights. On the right background the bokeh produced by this lens its actually quite pleasing. Bokeh color fringing was also observed in a picture of Christmas lights at f3.5. I personally like this effect, but I understand that some others do not.

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35mm f/3.5	35mm f/8
35mm f/3.5	35mm f/8
35mm f/4	35mm f/5.6
35mm f/3.5

This lens has excellent color reproduction. Reds, blues, and purples come out very saturated and almost seem to pop out to the image. This lens is capable of preserving the subtle color tones seen in flowers and other colorful objects better then most other lenses I have used. Other colors are also reproduced very well, but this lens seems to favor Reds and blues more so then greens and yellows. If color is what you are after, this is the lens that will produce.

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35mm f/11

35mm f/8